@potatosord Because that's how video games, and unfortunately real life work. People assign rarity to things that are scarce/not easily attainable by others. It's the same reason why gold, diamonds, other gem stones, etc are so expensive, it's the same reason why there are literal pieces of cardboard worth hundreds of thousands of dollars, the same reason why Bentley cars are half a million or more - rarity/scarcity.
Is it good overall? I'm not really knowledgeable enough to say. But what I can say is that people are raised in this scenario of scarcity, and grow to believe in and value the things they work hard for. That's the reason people are upset; they worked for these cosmetics when they were rewards for current content, and are now being practically given away.
We can discuss FOMO being good or bad until we turn purple, but it's part of life whether we like it or not - sometimes things happen and we miss out on unique opportunities, but unlike in real life, gamers clamor for unlimited chances at getting x or y unique item.
You say it's a "sad type of superiority" to want to maintain uniqueness for items, but I say it's a sad type of entitlement to be expected to be given everything to you on a silver platter, regardless if you've earned it or not, simply because you want it. You say that a video game is meant to be enjoyed, to which I agree - but let me ask this; why is your enjoyment of a game hindered/barred because you're unable to have full access to some cosmetics you weren't around for?
Do you also go to Taco Bell and demand that they make you the discontinued chicken taquitos, nacho fries, or spicy gordita crunch wraps, and then get huffy when they won't make it? So why are video games different? It's the same principle, yet people expect video games to be somehow absolved of FOMO, when the rest of the world practically runs on it.